After nurturing an alien life form (and then fighting it when it turns on them), the astronauts of the International Space Station are forced to make a last-ditch effort to stop the creature known as Calvin.

But in the final moments of the film, viewers learn that Calvin has made his way to Earth, via David Jordan's (Jake Gyllenhaal) escape pod. Meanwhile, in a twist on horror's final girl trope, Miranda North (Rebecca Ferguson) is last seen heading to her doom in deep space in the pod viewers had assumed had made it home.

The disturbing ending is part of why director Daniel Espinosa wanted to work on the project, and he says part of his conditions for signing on were that it not be changed. In a conversation with Heat Vision, he also talks about the film's most disturbing scenes (drowning in space) and challenging moments (that long opening one-shot).

Was there ever going to be a happy ending?

It was shot to be realistic. It was a shot to make a science fiction movie that ties into this other great American genre, which is noir. Many of the fundamental alphabets that we have in cinema were created in the noir era ... When I met the producers, I told them, "I completely understand that this ending might not be the preferable choice, but for me it was a fundamental part of the reason I want to do the movie." If we couldn't see eye to eye with the ending, we should part ways before we get something started. My producers were completely supportive, which I thought was surprising and bold.

Early on, you as a viewer love Calvin. He's beautiful. What was your inspiration for his look?

He's a baby. There's a great photographer who takes still pictures of kids when they are in the stomach. They have this glowing. That's what I gave Calvin. To connect to the fundamental idea of life's origin.

We lose Ryan Reynolds' character early on. It made me realize anything can happen in this movie. What does killing the most charismatic character early on do for the movie?

There are many things to point to the idea that [the film] resembles Alien. There are two things that differentiate it. One was that turn, which is very noir. And the ending is very noir. Those horrible endings in noir movies from the '50s. They are great, I loved them. I thought to myself, to pursue this noir idea, I have to have my Janet Leigh. Ryan became my Janet Leigh.

Drowning in space is likely going to be an enduring image from this movie. How did you get that right?

It comes from something that really happened. An Italian astronaut [nearly] drowned in his suit. It's so poetic that you are in this vast space and you are succumbed by something we believe is so Earth-bound, which is the fear of drowning. To do that was very technically problematic. Just creating water in zero gravity, how does it look, how does it feel? I thought all deaths have a fundamental fear inside of them. If it's claustrophobia, if it's rape, so I wanted those kinds of fundamental fears to tap into the audience's psyche.

For people, it's a fun ride and all of that. It's not just about the dangers. As a director, you have to have these kinds of ideas, to make your picture.

Was there anything in the script that was really hard to get right?

What got me to America was a gangster movie, Easy Money. The gangster movie has a great tradition of late, and that's the oner. There's only one other genre that has the oner. When I did EasyMoney, one great kind of failure for myself was that it didn't have a oner. I wanted to fulfill the genre idea and break the rules when I have to, but fulfill parts of them. And it felt unfinished. When I got this, I thought, "What if I do the whole open as a oner? What if that is the introduction to these characters?" And gets people to understand that the space station is like the intestines that you are swimming through. To very classically set the stage. And then I thought, "I'm mad." How can I do that? It's eight minutes. But then I started planning it. It becomes a technical achievement.

What was that the toughest part?

The oner was a monstrosity because in many ways, I wanted the inverse version of Gravity. Gravity looks at the vastness of space through the oner. I wanted to look at the claustrophobia. That made it quite daunting to get the camera through these spaces and having the performers and the rhythm. What we did is, we put music over it to get the right rhythm. I had the music composed before we started shooting. Because it was noir, I asked the composer to write something that had had a Bernard Herrmann in it. Then I told them my favorite movie of all time in space in 2001, so I wanted Bernard Herrmann meets [Gyorgy] Ligeti.

These characters were distinct. What were some of the things you told these actors that helped them learn who they were? They seemed real.

I just went into who they were and tried to construct a life story that was based on things I know. With Miranda North [Ferguson], she's from the CDC. I met the leader of the CDC when I was 21 years old. Anthony Fauci. Anthony Fauci is maybe the scariest person I've ever met in my life. Really. He's like a J. Edgar Hoover. He's one of those who that started the CDC. Anthony Fauci's main job is looking into what can go wrong. When I met him, when he looked at me he thought, "What can go wrong?" That was terrifying for me. I was 21 and holding a camera and was trying to do a documentary about HIV and this man looked at me and he could see all my flaws, immediately. Miranda North is his favorite pupil. So who is she? Who is this person that Anthony Fauci actually respects? And thinks is worthy of this task? And what makes a woman become that person? What is it in her back story that made her have the same sensibility as a 60-year-old man? So there was a life story for her. I gave each of them [the cast] clues, and they were not allowed to talk to each other about them. So they all had this sensational secret that they knew about themselves that nobody else knew.